The present invention generally relates to ground anchoring systems for supporting building foundation structures, and more particularly to raised floor foundation systems with helical piles or small diameter pile foundation systems, commonly used at building sites having moderately to highly expansive soil conditions.
A number of factors, including the diminishing availability of residential lots having good soil conditions and topography, have forced builders of residential housing to consider building sites that are more challenging to build on, and that require special foundations and anchoring systems. This includes geographic regions in the United States having highly expansive clay soils, such as the desert areas of Arizona and Nevada. The fast-growing Las Vegas area is an example. There the buildable land is flat, but has moderate to highly expansive and corrosive soil conditions. As a result, most homes in the Las Vegas area have been built with ground floors and foundations in the form of pre-stressed, post-tensioned mat slabs. In such building systems, the foundation slab is approximately 10″ to 18″ thick, with thickened (deepened) edge beams. While mat slabs are cost-effective when building on soils that have little or no expansivity, the cost of using mat slabs in expansive soil conditions is substantial, due to the necessity of eliminating the uplifting forces on the slab caused by the expansivity of the soil. Typically, three or more feet of soil must be removed, reconditioned by moisture treating and then compacted in place. If the soil is highly expansive or corrosive, the soil may need to be removed altogether and replaced with an imported soil material. Environmental concerns associated with the additional earth work may further add to the cost.
Due to the cost associated with mat slab systems, homebuilders who build in highly expansive soil conditions, and particularly homebuilders in the Las Vegas area, frequently use raised floor foundation systems with helical anchors. However, such systems have a significant drawback, in that, they provide a relatively low degree of lateral support for the foundation system for resisting lateral forces such as produced by earthquakes or high winds. Therefore, a need exists for a way to increase the lateral resistance capacity of conventional anchoring systems used for raised foundations in expansive soils. A need also exists for a lateral force resistance device that can be used with standard anchoring systems, that is relatively economical to manufacture, and that is relatively easy to install.